Managing Exceptions

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By default, Wing's debugger stops at exceptions when they would be printed by the Python interpreter or when they are logged with logging.exception. Wing will also stop on all AssertionError exceptions, whether or not they are printed or logged, since these usually indicate a program error even if they are handled. These behaviors can be altered with the Debugger > Exceptions preference group, as described below.

Ignoring Exceptions

Individual exceptions can be ignored by checking the Ignore this exception location check box in the debugger's Exceptions tool and continuing debug.

This is useful in ignoring non-critical exceptions that are being raised by code that is not currently of interest, in order to be able to work on other problems.

Ignored exceptions are remembered in the project and may be cleared with Clear Ignored Exceptions in the Debug menu.

Ignored exceptions are still reported if they actually lead to program termination.

Exception Reporting Mode

The overall strategy for identifying and reporting exceptions is configured with the Debugger > Exceptions > Report Exceptions preference. The following choices are available:

  • When Printed stops on exceptions at the time that they would have been printed out by the Python interpreter. This is the default.

    For code with catch-all exceptions written in Python, Wing may fail to report unexpected exceptions if the handlers do not print the exception. In this case, it is best to rewrite the catch-all handlers as described in Trouble-shooting Failure to Stop on Exceptions.

    Note that in this exception handling mode, any code in finally clauses, except clauses that reraise the exception, and with statement cleanup routines will be executed before the debugger stops because they execute before the traceback is printed.

  • Always Immediately stops at every single exception immediately when it is raised. In most code this will be very often, since exceptions may be used internally to handle normal, acceptible runtime conditions. As a result, this option is usually only useful after already running close to code that requires further examination.
  • At Process Termination makes a best effort to stop and report exceptions that actually lead to process termination. This occurs just before or sometimes just after the process is terminated. The exception is also printed to stderr, as it would be when running outside of the debugger.

    When working with an Externally Launched Debug Process , this mode may not be able to stop the debug process before it exits, and in some cases may even fail to show any post-mortem traceback at all, except as printed to stderr by the debug process.

Reporting Logged Exceptions

The Debugger > Exceptions > Report Logged Exceptions in When Printed Mode preference controls whether exceptions that are not printed but that are logged with a call to logging.exception will be reported by the default When Printed exception reporting mode. This preference is ignored in other exception reporting modes.

Exception Type Filters

The Debugger > Exceptions > Never Report and Debugger > Exceptions > Always Report preferences can be used to specify that certain exception types should never be reported at all, or always reported regardless of whether they are printed or logged. For example, by default Wing will never stop on SystemExit or GeneratorExit since these occur during normal program behavior, and Wing will always stop on AssertionError since this usually indicates a bug in code even if it is handled.

In some code, adding NameError or AttributeError to the Always Report list may help to uncover bugs that are being masked by overly broad exception handlers. However, this will not work if these are treated as normal expected exceptions. This is common enough that they are not included in Wing's default Always Report list.